1. Field of the Invention
The present invention relates to a system controlling device and an image processing system.
2. Description of the Related Art
Generally, an image processing system such as a digital multifunction product (MFP) that processes image data includes units interconnected by parallel buses such as PCI buses. For example, Japanese Patent Application Laid-Open No. 2005-092770 discloses such a PCI bus connection.
FIG. 17 is an exemplary diagram of a system controlling unit 1000 in a conventional image processing system. The system controlling unit 1000 manages transfer of a large volume of image data between a plurality of units (devices), and, in an input-output mechanism of the image processing system, controls an input-output (I/O) device 2000 such that it can perform functions such as scanning and printing.
To achieve high-speed image processing in the image processing system, it is necessary to increase the operating speed of a central processing unit (CPU) 1001 or an external memory 1002. Similarly, to enable use of applications requiring high computational capacity and enhance connectivity between the units, it is necessary to speed up the flow of data (internal bandwidth) such as image data and control commands.
However, connecting the I/O device 2000 and the system controlling unit 1000 by a parallel PCI bus restricts high-speed transfer of a large amount of data.
For example, consider a case when the I/O device 2000 and the system controlling unit 1000 are connected by a 64-bit/33 MHz PCI bus. The actual bandwidth of the PCI bus is about 50% of the theoretical value, i.e., 64 bits×33.3 megahertz×0.5, which comes to about 130 MB/s. Meanwhile, to transfer eight-bit red-green-blue (RGB) scanned data of A4 size with 600 dots per inch (dpi) and having data compression ratio equal to one at a rate of one sheet of paper per second (no interval between sheets), a bandwidth of 100 MB/s is required because eight bit RGB data of A4 size with 600 dpi amounts to about 100 megabytes. Similarly, to transfer four-bit cyan-magenta-yellow-black (CMYK) printed data of A4 size with 600 dpi and having data compression ratio equal to one at a rate of one sheet of paper per second (no interval between sheets), a bandwidth of 66.7 MB/s is required because four-bit CMYK data of A4 size with 600 dpi amounts to about 66.7 megabytes. Hence, considering the actual bandwidth of the PCI bus, it is not possible to transfer the data at the rate of one sheet of paper per second unless a lighter data format is used or processing speed is reduced.
On the other hand, in case of a laser MFP having identical configuration as shown in FIG. 17, the data transfer needs to be in synchronization with the operations of the I/O device 2000. Moreover, to cut down the system cost, it is necessary to remove a memory 1007 connected to an application specific integrated circuit (ASIC) 1004 such that only one memory is used, viz., the external memory 1002 connected to a memory control hub 1003.
However, to perform the data transfer in synchronization with the operations of the I/O device 2000, it is necessary to extensively increase the bandwidth of an accelerated graphics port (AGP) bus connecting the ASIC 1004 and the memory control hub 1003. Hence, conventionally, the memory 1007 is used in addition to the external memory 1002 such that the need of data transfer related to copy processes through the AGP bus is eliminated, which results in securing a sufficient bandwidth.
For example, consider a case when the ASIC 1004 and the memory control hub 1003 are connected by an AGP x4 bus. The actual bandwidth of that AGP x4 bus is about 50% of the theoretical value, i.e., 32 bits×66.6 megahertz×4×0.5, which comes to about 500 MB/s. In the case where only the external memory 1002 is used by removing the memory 1007, the 500 MB/s becomes the upper limit of the bandwidth. Meanwhile, as described above, a bandwidth of 100 MB/s is required to transfer eight-bit red-green-blue (RGB) scanned data of A4 size with 600 dots per inch (dpi) and having data compression ratio equal to one at a rate of one sheet of paper per second (no interval between sheets). Moreover, a bandwidth of 100 MB/s is required to read the scanned data from the external memory 1002 and store it in a hard disk drive (HDD) 1006 via the memory control hub 1003 and the ASIC 1004. A bandwidth of 133.3 MB/s is required for the ASIC 1004 to read four-bit CMYK printed data of A4 size with 600 dpi from the external memory 1002, perform rotation on the data, and restore the rotated data in the external memory 1002 (four-bit CMYK data of A4 size with 600 dpi amounts to about 66.7 megabytes. Hence, 66.7 MB/s+66.7 MB/s=133.3 MB/s). A further 100 MB/s is required for the ASIC 1004 to re-read the rotated data from the external memory 1002, compress the data (data compression ration=2), and restore the compressed data in the external memory 1002 (66.7 MB/s+66.7 MB/s÷2=100 MB/s). Furthermore, when the compressed data is to be transferred to the I/O device 2000 at the rate of one sheet of paper per second (no interval between sheets), a bandwidth of 33.3 MB/s is required for the ASIC 1004 to read the data and decompress it (66.7 MB/s÷2=33.3 MB/s). Thus, the total required bandwidth amounts to:100 MB/s+100 MB/s+133.3 MB/s+100 MB/s+33.3 MB/s=466.6 MB/s
That is, more than 90% of the actual bandwidth of the AGP x4 bus is required for the abovementioned processing. Hence, the maximum possible rate of data transfer is about one sheet of paper per second. To increase the rate of data transfer, i.e., to enhance the productivity of the image processing system, it is necessary to use a lighter data format or reduce processing speed requirements.